Programmed death ligand-1 expression and memory T-cell generation in Coxiella burnetii infection.

Programmed death ligand-1 (PD-L1) is a co-signaling molecule that regulates T-cell responses in vivo. Its role in bacterial infections, including Q fever, a zoonosis due to Coxiella burnetii infection, is not well understood. We showed by flow cytometry that PD-L1 membrane expression was specifically increased in T-cells from patients with acute Q fever, not from patients with Q fever endocarditis, suggesting that PD-L1 plays a role in the early phases of C. burnetii infection. To assess this hypothesis, we studied the role of PD-L1 in C. burnetii-infected mice. C. burnetii infection resulted in PD-L1 up-regulation in splenocytes. Anti-PD-L1 antibodies injected into the mice did not affect the total number of splenic T-cells but increased the relative number of CD4(+) T-cells compared with CD8(+) T-cells. Additionally, anti-PD-L1 antibodies significantly increased the number of splenic CD4(+) and CD8(+) T cells that expressed low membrane CD62L levels. Our results indicate that the increased expression of PD-L1 by T-cells is associated with a decreased number of memory T-cells during C. burnetii infection, opening new perspectives in the understanding of Q fever pathophysiology.